Provide a way to specify an attachment disposition

Some cursory code reviews:

• The module also has an implicit dependency on the path_alias module in the Controller, so should probably be declared in the module dependencies definition.
• The $response object initially created here is no longer used.

To make sure this ticket doesn't include too much I opened

#3295337: Create config schema
#3295338: Update module dependency to include path_alias

Thanks for the relatively quick fix!

To implement something like media_entity_download think we would need to extend the image formatter most likely with one of these hooks

Haha, I wasn't even thinking that far ahead, I was just thinking of having a query string like ?attachment or ?dl detected in the controller which determines whether the media item should be forcefully downloaded as an attachment when necessary even if the browser can typically open it inline just fine (aka., the current default behaviour, which I'm fine with).

The media entity may contain documents and archives file rather than images, so the image formatter approach might not be a feasible solution (unless I'm misunderstanding the scope of the implementation).

media_entity_download implements its own formatter to address a similar issue to this, I don't personally need a one size fits all disposition for all media entities, I think it makes sense for it to be on an entity by entity basis, by specifying the query string where necessary (and is more of a power user tool).

Nope, that all makes sense to me :)

I didn't wanna update the PR without first getting feedback from you, so I've added some of my thoughts on the PR to get your input on them.

I also made some changes and had the tests failing locally, so didn't wanna push them up until I had time to debug why.
Most of the changes were pretty innocent, so was slightly interesting to see the tests fail.

I fixed the initial failed test (I think this is the one you're also having) which were because all calls to $this->createMedia(); essentially share the same underlying file entity internally, so after unlinking it here, subsequent calls to it will have the file missing from disk and lead to inconsistent behaviour, the files need to be unique per $this->createMedia(); call.

I then ran into another issue with the failed test when I introduced custom path aliases to ensure the behaviour was still consistent with or without aliases, this is what I have in my backlog to fix before I push up.

And lol, slightly interesting to see @immaculatexavier supposedly made their first commit to this issue’s fork and was given a draft credit, but there's no actual commits. Wonder what happened there.

Fixed the broken test cases, it was related to the test case reusing the same test file internally (especailly during deletions), as well as $this->file, which meant the test was referencing the wrong file instance while doing its comparisons. I've moved the references into local variables with appropriate names, as well as removed reliance on the path_alias module.

It shouldn't be necessary for this to work since the controller shouldn't be concerned with the alias at that point. It should've already resolved the media entity it's working with.

The change introduces a bunch of other minor improvements, so I've added them in a new branch for review/cherry-picking purposes.